This invention relates to supramolecular polymers comprising quadruple hydrogen bonding units that are capable of forming at least four H-bridges with each other leading to physical interactions between different polymer chains. The physical interactions originate from multiple hydrogen bonding interactions (supramolecular interactions) between self-complementary units comprising at least four hydrogen bonds in a row. Units capable of forming at least four hydrogen bonds, i.e. quadruple hydrogen bonding units, are in this patent application abbreviated as 4H-units, 4H-elements or structural elements (4H) and are used in this patent application as interchangeable terms. Sijbesma et al. (U.S. Pat. No. 6,320,018; Science, 278, 1601; incorporated by reference herein) discloses such self-complementary units which are based on 2-ureido-4-pyrimidones.
Telechelic polymers or trifunctional polymers have been modified with 4H-units (Folmer, B. J. B. et al., Adv. Mater. 2000, Vol. 12, 874; Hirschberg et al., Macromolecules 1999, Vol. 32, 2696; Lange, R. F. M. et al, J. Polym. Sci, Part A, 1999, 37, 3657-3670). However, these polymers have the 4H-unit coupled at the ends of the polymers, so the number of end groups is therefore limited by the amount of end groups (normally 2), and the functional units are always located on the periphery of the polymer.
Polymers containing hydrogen bonding groups grafted on the main chain that are synthesized via copolymerization of hydrogen bonding monomers have been obtained with hydrogen bonding units containing three H-bonds in a row (Lange F. M. et al., Macromolecules 1995, Vol 28, 782). However, only an alternating copolymer of styrene and maleimide can be used in this approach, and moreover, the H-bonding interactions between the polymers are much weaker than the H-bonding based on the 4H-units, obviously resulting in poorer material properties.
Polymers with quadruple H-bonding units grafted on the main chain have been obtained by copolymerizing an olefin bearing a 4H-unit with a common olefin (Coates, G. W. et al., Angew. Chem. Int. Ed., 2001, Vol. 40, 2153). However, complex chemistry has to be used to prepare and to polymerize the monomer and, due to the intrinsic sensitivity of the catalyst needed to obtain the polymer, severe limitations hinder the general use of this system and limits it to tailor-made polyolefin systems. For example, Coates et al. discloses the copolymerization of 1-hexene and a 6-hexenyl-2-ureido-4-pyrimidone derivative with a Ziegler-Natta type nickel based catalyst and diethylaluminum chloride as cocatalyst. Another drawback of the method according to Coates et al. is that the amount of 4H-units that can be incorporated in the copolymer is rather limited, i.e. typically about 2 mol %.
WO 02/46260 discloses polyurethane based polymers with H-bonding units as end-cappers and optionally grafted with H-bonding units that can be used as hot melt adhesive or TPU-foam. WO 02/098377 discloses polymers with H-bonding units as end groups that can be used in cosmetic compositions. Both patent applications use comparable or the same chemistry as described in the papers above.
U.S. Provisional Patent Application No. 60/403,636, filed Aug. 16, 2002, and PCT/NL03/00586, filed Aug. 15, 2003, incorporated by reference herein for the US patent practice, discloses simpler chemistry to acquire polymers with grafted quadruple H-bonding units. For example, polyacrylates and polymethacrylates with grafted 4H-units have been produced using different kinds of polymerization techniques.
U.S. Provisional Patent Application No. 60/431,712, filed Dec. 3, 2002, incorporated by reference herein for the US patent practice, discloses polysiloxanes comprising 4H-units in the polymer backbone. More precisely, polysiloxanes are disclosed having (a) 4H-units directly incorporated in the polymer backbone, wherein the 4H-units are incorporated via two linkers and are covalently attached through a silicon-carbon bond or (b) 4H-units pending from the polymer backbone, wherein the 4H-units are covalently attached via one linker through a silicon-carbon bond.
The present invention discloses polymers comprising 4H-units within the polymer backbone that can easily be prepared by chain extending a functional macromonomer with a functional monomer comprising a 4H-unit (or a precursor of such a unit). Alternatively, redistribution reactions of polymers with functional monomers comprising a 4H-unit can be employed. The invention allows for control over the average amount of 4H-units per polymer chain by setting the molar ratio between the reacting species.
The supramolecular according to the present invention are unprecedented, because they comprise multiple 4H-units as an integral part of the polymeric main chain. Also, the presented supramolecular polymers display unique material properties because of the reversible nature of the H-bonding interactions between the polymer chains, allowing reversible change of the material properties by external stimuli like heat or dilution. Consequently, it is possible to prepare materials that combine the mechanical properties of conventional macromolecules with the low melt viscosity of organic compounds. The presence of 4H-units in the polymer backbone is strongly beneficial, because the materials are easier to synthesize and/or result in superior material properties as compared to polymers comprising 4H-units that have been disclosed previously, such as 4H-units grafted on polymers or 4H-units attached to the end groups of polymer chains.